Rotating radio beacon



Aug. 26, A1941.

n. G. c. LUCK MICROF/[UNE ROTATING RADIO BEACGN sPzscH Filed June 22,193s PHE@ w n I 'f TED Po w51? bsc/LL/Wan F'mw. ,6

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[ILE/ER 1751775 Enom/Lara )ry/LIER (Aira F/L'rsn Las PHH'SE' IMD/61770)?David C. L aofi Bnuentor Cttorneg Patented Aug. 26, 1941 UNITED STATESPATENT OFFICE ROTATING RADIO BEACON David G. C. Luck, Haddon Heights, N.J., assignor to Radio Corporation of America, a corporation of DelawareApplication June 22, 1938, Serial No. l215,102

(Cl. Z50-11) -6 Claims.

I, modulation. A non-directive wave is radiated from an antenna at thecentral point. The rotating wave and the non-directive wave combine to`establish a substantially cardioid eld -which rotates about the centralpoint. 4The rotating field induces signal currents in a receivingantenna within the iield. The signal currents havev substantially asinelwave form. with phase vary-v ing directly with received azimuth.

If the phase o'f the sine wave is determined, the bearing of thereceiver with respect to the transmitter can be determined.y In order tomake such determinations, it is proposed, intheabove mentioned` patent,to key olf both fields at the instant when the maximum of the cardioidpasses through due North. In order to have a sharply defined referencesignal the keyingshould be of very short duration. In some lnstallationsabrupt keying is disadvantageous because the steep wave front of thereference'impulse corresponds to a wide. band-of frequencies, and a Widebandv is either not available or may interfere with speech'modulationswhich may be applied to the carrier wave.

In the instant invention, it is proposed to vavoid the aforementioneddiiiiculties .by establishing a double' modulation of the carrier `wave.The double modulation is equivalent to sub-carriers and their side bandswhich are arranged slightly beyond vthe speech frequency bands of themain carrier. The method of generating the reference phase'by `doublemodulation and receiving and demodulating will be morev fully discussedhereinafter.

Onel of the objects of this invention is to provide'means for doublemodulation in a rotating radio beacon transmitter wherebyy waves ofvarying andiixed` phases are established. 'An' other objectsisvv toprovide means for receiving double modulation signals from a rotatingbeacon transmitter,l and to, derive therefrom currents of Y. t iixed andvariable phases. Another object is to f Vprovidefmeans for establishingin a rotating radio fieldv a fixed reference phase by means ofsubcarriers which arelmodulated. A further ob.

ject is to provide means for receiving a wave of variable phase and acarrier wave including a sub-carrier which includes la reference phase.A still further object is to provide improved means for transmittingfrom a rotating beacon station Waves including speech, fixedphaseandvariable phase signals, and for receiving and separating saidsignals. l

'I'he invention will be described by referring to the accompanyingdrawing in which Figure 1 is a block diagram illustrating one iembodiment of the invention;

vFigure 2 is an illustration ofthe carrier and sub-carrier; and

Figure 3 is a block diagram of one form of receiver embodied in theinvention.

Referring to Fig. 1, an oscillator l is connected to a modulated poweramplifier 3, which is coupled to an antenna 5. The oscillator is alsoconnected to a pair of balanced'modulators 1, 9.

The balanced modulators are coupled to pairs of Adcock or otherdirective antennas Il, I3. The

' pliiier 3.

' w-i-(i-a) are established. The currents. alongv A second oscillator I5is connected to a modulated amplifier Il which is connected to themodulated power amplifier 3. Speech signals may be applied to themicrophone I9 and, through the speech amplifier 2|, to the modulatedpower am- A rthird oscillator 23 is connected through a phase shifter 22to the modulated amplifier i 1, directly to the first balanced modulatorl, and through the phase shifter 25 to the second balanced modulator 9,.The phase shifter 22 is adjusted to obtain a reference phase,corresponding, for example, to North.

The operation of the transmitter is as follows:

-The oscillator l generates carrier frequency currents of frequency'wwhich are amplified and modulated by currents from the second and thirdoscillators l5, 23 to thereby establish radio fre- The secondl and thirdoscilwith the carrier and the carrier i speech frequency currents, areapplied to the central antenna 5 from ywhich non-directive fields areradiated. The third oscillator, which generates cur- 'There-- lmodulators,

rents of frequency e, applies these currents in phase quadrature to thepairs of balanced modulators. The balanced modulators 1. 9 apply thecurrents of side band frequency wie: and

wia/90 and the speech frequencyside bands are illustrated in Fig. 2. Itmay be observed that the frequencies a are made lower than speechfrequencies and the sub-carriers are higher than the frequenciesrequired for speech transmission. The arrangement makes it practical toapply the rotating beacon and telephonie transmission to a singlechannel of comparatively narrow range.

The reception is effected by receiving the several signals on a radioreceiver 21 which includes a demodulator, and an amplifier. The outputof the amplifier is connected to a speech frequency filter 29, a secondlter (ia) 3|, and third filter (a) 33. The output from the first filter29 is applied to telephone receivers 35. The second filter 3| isconnected to a demodulator 31 which is connected to a fourth filter (a)39. The outputs from the third filter 33 and the fourth lter 39 areapplied to a phase indicator 4|.

The operation of the receiver is as. follows:

- The received radio signals, after amplification,

demodulation and, if desired, further amplification, include currents ofspeech, double modulation (ia), and modulation (a) frequencies. Thecurrents of the several frequencies are separated by filters 29, 3|, 33of appropriate design. The currents of double modulation (ia) aredemodulated to obtain the current of fixed reference phase a, whichafter filtering is applied to the phase indicator. quency a are obtainedfrom the rotating fields (wl-a) and the current oi.' reference phase isobtained from the non-directive double modulation (ia), it follows thatone phase is fixed and the other phase is a function of the bearing ofthe receiver.

Thus a rotating radio beacon system has been described. The transmitteris characterized by its use of a single channel for transmitting speech,double modulation and a rotating cardioid field. The double modulationincludes a component of fixed phase which serves as a reference fordetermining the phase of the rotating cardioid. Reception is obtained byfiltering the several currents after demodulating in the receiver andeffecting a second demodulation to derive the reference phase which iscompared to the signal phase to determine bearing. The details of theoscillators, modulators, balanced filters and the like have been omittedbecause these elements are generally well known to those skilled in theart. Furthermore, reference is made tothe above mentioned patent whichdescribes the preferred elements which have been employed in practice.

I claim as my invention:

1. The method of directional transmission which includes radiating anon-directive carrier wave, modulating said carrier with a modulatedsub-carrier of frequencies beyond the speech fre- Since the currents offrequency band, further modulating said carrier waveby speechfrequencies, and radiating a directive rotating field of the samecarrier frequency as the non-directive carrier and rotating at theangular velocity of said sub-carrier modulation frequency.

2. The method of directional transmission which includes generatingcarrier frequency energy, modulating said energy with energy from amodulated sub-carrier of a frequency higher than speech frequencies,modulating said carrier with speech frequencies, radiating said doublemodulated carrier energy. deriving two phases of energy. of saidsub-carrier modulation frequency, modulating said carrier frequencyenergy by said two phase energy and separately radiating said lastmentioned energy in differently directed patterns.

3. 'Ihe method of`determining bearings by radio which includes radiatinga non-directional carrier wave, modulating said wave by a modulatedsub-carrier of a frequency higher than speech frequencies, furthermodulating said carrier wave with speech frequencies, rotating aradiated directional wave of the samevcarrier frequency as saidnon-directional carrier wave and rotating at the angular velocity ofsaid subcarrier modulation frequency, receiving said non-directional anddirectional waves of the same carrier frequency, demodulating saidwaves, deriving from said demodulated waves. currents of speechVfrequencies, deriving from said demodulated waves, currents of fixedreference phase, deriving from said demodulated waves, currents whosephase varies as a function of the bearing of the receiver anddetermining the difference of said phases.

4. In a rotating radio beacon the combination of a carrier frequencygenerator, means for modulating currents from said generator bymodulated sub-carrier currents, said sub-carrier having a frequencyhigher than speech frequencies, and said modulation being lower thanspeech frequencies, means for modulating said carrier with speechfrequencies, means for radiating said compoundly modulated carrier,means for establishing'currents of two phases of the frequency of saidsub-carrier modulation, modulation means for modulating said carrier bysaid currents of two phases, and antennas for separately and directivelyradiating the last mentioned modulated carrier.

5. In a rotating radio beacon, a first generator of carrier frequencycurrents, a second generator of sub-carrier currents. a third generatorof modulation frequency currents, a fourth generator of speech frequencycurrents, means for modulating said sub-carrier currents by saidmodulation frequency currents, means for modulating said carriercurrents by said modulated subcarrier and speech frequency currents, anon-directive antenna, means for applying the .thus modulatedy carriercurrents to said nondirective antenna, directive antennas, means formodulating said carrier frequency currents with said modulationfrequency currents, and means for applying said last mentioned modulatedcarrier currents to said directive antennas for radiating therefrom arotating field.

\ 6. In a beacon of the character of claim 5, a

phase shifter connected between said third generator and saidsub-carriermodulating means.

DAVID G. C. LUCK.

